Heat pipe heat exchanger

ABSTRACT

Being a heat pipe heat exchanger wherein a group of heat pipes are arranged in box form and the central part thereof is partitioned, a high temperature fluid being let to flow into one and a low temperature fluid into the other one, respectively, so that, by the specific properties of the heat pipes, the heat given from the high temperature fluid is transferred to the low temperature fluid through the sealed-in fluid in the heat pipes, a plurality of heat pipes of which those on at least the high temperature fluid passage side are bare pipes are arranged to extend over both passages, and the heat pipes on the high temperature fluid passage side are inserted in finless outer pipes. At least the outer surface of these finless outer pipes is treated for resistance to corrosion. Also, these finless outer pipes and the heat pipes are joined by a heat conductive material, so that heat pipes can be easily demounted, and, therefore, the efficiency of the heat exchanger can be varied as required.

TECHNICAL FIELD

The present invention relates to a heat pipe heat exchanger.

BACKGROUND TECHNIQUE

Heretofore, various types of heat exchangers utilizing heat pipes whichtransfer heat from a high temperature fluid to a low temperature fluidhave been developed.

As a typical one thereof, a fixed-type heat pipe heat exchanger is knownwherein a group of heat pipes are arranged in box form and the centralpart thereof is partitioned, a high temperature fluid being let to flowinto one and a low temperature fluid into the other one, respectively,so that, by the specific properties of the heat pipes, the heat givenfrom the high temperature fluid is transferred to the low temperaturefluid through the sealed-in fluid in the heat pipes.

However, if this kind of fixed-type heat pipe heat exchanger is used torecover heat effectively from the combustion gases containing dust,sulfur oxide (SO_(x)) and nitrogen oxide (NO_(x)) at high concentrationexhausted from large-sized boilers or industrial furnaces forsteam-power plant, then, as shown in FIG. 1, these dust and the likeadhere to the gaps of a number of fins 2 attached to the outside of heatpipes 1 on the high temperature side to blockade the passage for thehigh temperature gas, and, also, the surface temperature of the heatpipes on the high temperature fluid side drops below the acid dew pointtemperature of the exhaust gas, so that the sulfuric acid content in theexhaust gas condenses to adhere to the surface of the heat pipes, thishaving been the cause of corroding the heat pipes.

Accordingly, the present invention, being one accomplished in view ofthe above-mentioned circumstances, has for its object the providing of afixed-type heat pipe heat exchanger which can be used to recover heatfrom the combustion gases containing dust, sulfur oxide (SO_(x)) and thelike at high concentration exhausted from a large-sized boiler or thelike of a steam-power plant and utilize the heat effectively, andwherein the gas passages are not blocked up by dust and the like and yetthe heat pipes are not corroded by the sulfuric acid content in theexhaust gas.

DISCLOSURE OF THE INVENTION

That is to say, the present invention lies in a heat pipe heat exchangerwherein a passage for low temperature fluid and a passage for hightemperature fluid are formed respectively by a partition wall and aplurality of heat pipes of which those on at least the high temperaturefluid passage side are bare pipes are arranged to extend over bothpassages, the heat pipes on the high temperature fluid passage sidebeing inserted in finless outer pipes.

BRIEF EXPLANATION OF THE DRAWING

FIG. 1 is an explanation of the conventional general fixed-type heatpipe heat exchanger,

FIG. 2 shows an entire flow sheet of one embodiment of the heat pipeheat exchanger of the present invention, wherein the numeral 15represents the heat pipe heat exchanger of the present invention, and

FIGS. 3 and 4 are diagrams of the embodiment of the heat pipe heatexchanger of the present invention.

BEST MODE FOR WORKING THE INVENTION

To expound the present invention in more detail, an explanation is givenhereunder following the accompanying drawing.

FIGS. 2, 3 and 4 show one embodiment of the present invention, FIG. 2being an example of arrangement of the heat pipe heat exchanger 15 ofthe present invention disposed before and after a wet-type desulfurizer14 for boiler exhaust gas.

The combustion air for boiler 12 supplied by a forced-air blower 10 isfirst preheated in an air preheater 11 and then supplied to a boiler 12.The exhaust gas from the boiler 12 which uses sulfur-containing fuelssuch as coal or heavy oil is passed through the air preheater 11 and adust collector 13 and is fed as a high temperature fluid for the heatpipe heat exchanger 15. The gas temperature at the high temperaturefluid inlet duct which varies with operating conditions such as boilerload and the like and overall design requirements is usually from 130°to 170° C. or thereabouts, which is lowered in the heat pipe heatexchanger to from 70° to 110° C. or thereabouts, and thereafter the gastemperature is further lowered in the wet-type desulfurizer 14 to from40° to 60° C. or thereabouts.

The gas leaving the wet-type desulfurizer is fed to the heat pipe heatexchanger as a low temperature fluid for the heat pipe heat exchanger15, to have its temperature increased to a sufficient level to preventthe corrosion of the stack or the formation of white smoke and toincrease the dispersion of the stack gas, and, thereafter, the gas isdischarged through the stack. The acid dew point temperature of theboiler exhaust gas at the high temperature fluid inlet duct in this casenecessarily varies with the kind of the boiler fuel, the combustionconditions and the like, but it is in many cases usually from 100° to150° C. or thereabouts, so that the surface temperature of all or a partof the heat pipes on the high temperature fluid passage side of the heatpipe heat exchanger is lower than the acid dew point temperature.

Under such environmental conditions, the heat pipes in the conventionalgeneral heat pipe heat exchanger are corroded by the sulfuric acidcontent in a very short time, but the heat pipe heat exchanger of thepresent invention causes no problem of corrosion or blockade and thelike due to dust and the like, so that the use for a long period becomespossible.

FIGS. 3 and 4 show the embodiment of the present invention. Heat pipes 1on the high temperature fluid passage side are bare pipes, which areinserted in finless outer pipes 4 having an enamel coat applied to theouter surface as a treatment for resistance to corrosion. Also, thesmall gaps between the heat pipes and the finless outer pipes are filledwith heat conductive grease as a heat conductive material 5, which actsto effectively transfer the heat given from the high temperature fluidto the heat pipes through the finless outer pipes. Under theabove-mentioned corrosive conditions at below the acid dew pointtemperature, the surface of the outer pipes is in many cases in the wetstate, so that dust and the like easily adhere to and collect on theirsurface, and, therefore, use is made of the finless outer pipes to makeit possible to remove the dust and the like easily by air blasting orwashing with water, and, in the present embodiment, the outer surface ofsaid finless outer pipes is provided with an enamel coat having a smoothsurface to improve the resistance to corrosion and the anti-blockadegreatly.

Generally, as metallic materials of high resistance to corrosion, thereare special alloys, but they are often expensive. The enameled outerpipes of the present invention are superior in resistance to corrosionand inexpensive.

As another advantage of using the finless outer pipes, incidentally inaddition to the above-mentioned advantages, in the case where thenecessity arises to replace the finless outer pipes or the heat pipesfor some reason such as the use for a long period or the like, they canbe replaced easily since the finless outer pipes and the heat pipes arejoined by a heat conductive material alone, and, at the same time, it ispossible, by joining the finless outer pipes with the partition plate 3,to seal the high temperature fluid and the low temperature fluid easily.

UTILIZABILITY IN INDUSTRY

As above, the heat pipe heat exchanger according to the presentinvention has many advantages as follows:

(1) The material for the heat pipes themselves may be different from thematerial for the finless outer pipes, so that, by selecting the materialfor the finless outer pipes that is suitable for a high temperaturefluid, it is possible to lighten the load for the corrosion or the likeof the heat pipes themselves.

(2) By applying a treatment for resistance to corrosion to the finlessouter pipes, a heat pipe heat exchanger which is far superior inresistance to corrosion is realized, so that the use for a long periodbecomes possible.

(3) By making the outer pipes finless, dust and the like which adheredto and collected on the finless outer pipes can be easily removed by airblasting or washing with water, so that a heat pipe heat exchanger whichis superior in anti-blockade is realized.

(4) By applying an enamel coat as a treatment for resistance tocorrosion to the finless outer pipes, a heat pipe heat exchanger isrealized which, in addition to having both resistance to corosion asmentioned in 1 above and antiblockade as mentioned in 3 above, ismoderate in prince and the outer surface of the finless outer pipes ofwhich is smooth, so that the adhesion of dust and the like is alsolowered and the removal thereof is easy.

(5) The heat pipes and the finless outer pipes are joined by a heatconductive material, so the heat pipes can be easily demounted, and,therefore, the efficiency of the heat exchanger can be varied asrequired.

(6) It is possible, by joining the finless outer pipes with thepartition plate, to easily effect the sealing of high temperature fluidand low temperature fluid.

We claim:
 1. A heat pipe heat exchanger comprising:a low temperaturefluid passage and a high temperature fluid passage defined by apartition board; a plurality of heat pipes extending over the entirewidth of said passages, said heat pipes being bare at least at the hightemperature fluid passage side; finless outer pipes coated at the outersurface with enamel for corrosion protection, said heat pipes at thehigh temperature fluid passage side being removably inserted into saidfinless outer pipes; and a heat conductive material disposed betweensaid heat pipes and said finless outer pipes.
 2. A heat pipe heatexchanger as described in 1 of the scope of demand characterized in thatsaid low temperature fluid and high temperature fluid are both gases. 3.A heat pipe heat exchanger as described in 1 or 2 of the scope of demandcharacterized in that at least the outer surface of said finless outerpipes is treated for resistance to corrosion.
 4. A heat pipe heatexchanger as described in 3 of the scope of demand characterized in thatsaid treatment for resistance to corrosion is effected with enamel.
 5. Aheat pipe heat exchanger as described in 1, 2, 3 or 4 of the scope ofdemand characterized in that a heat conductive material is inserted inbetween said finless outer pipes and heat pipes.